1. Field of the Invention
The present invention relates to an equalizer, an equalization method, a program and a receiving device, and particularly, relates to an equalizer, an equalization method, a program and a receiving device capable of certainly removing multipath interference by using a replica of a multipath component.
2. Description of the Related Art
Under an environment in which multipath occurs, the amplitude and the phase of a signal differs at the time of transmission and at the time of reception under the influence of multipath when the signal is transmitted. Accordingly, it is necessary to perform signal equalization at the reception side so that the amplitude and the phase of a received signal become equal to the transmitted signal.
As a common method of equalizing the received signal which has received the multipath inference in a time domain, a method of removing a multipath component by generating a replica of the multipath component and subtracting the generated replica from the received signal is known.
FIG. 1 is a diagram showing a configuration of an equalizer of related art which removes the multipath component from the received signal.
An equalizer 1 includes a variable coefficient FIR filter 11, a delay unit 12, a subtraction unit 13 and a variable coefficient IIR filter 14. A time-domain received signal obtained by A/D (Analog/Digital) conversion processing, synchronous processing and the like in a former-stage circuit is inputted to the variable coefficient FIR filter 11 and the delay unit 12.
The variable coefficient FIR filter 11 generates a replica of a multipath component (hereinafter, referred to as an advancing wave) arriving earlier than a dominant wave by performing filtering using a coefficient generated by a not-shown coefficient update circuit. The advancing-wave replica generated by the variable coefficient FIR filter 11 is supplied to the subtraction unit 13.
The delay unit 12 delays the time-domain received signal so that the advancing wave of the time-domain received signal and the advancing-wave replica outputted from the variable coefficient FIR filter 11 are supplied to the subtraction unit 13 at the same timing, outputting the signal. The time-domain received signal outputted from the delay unit 12 is supplied to the subtraction unit 13.
The subtraction unit 13 removes or suppresses the advancing-wave component included in the time-domain received signal by subtracting the advancing-wave replica generated by the variable coefficient FIR filter 11 from the time-domain received signal supplied from the delay unit 12. The time-domain received signal generated by the subtraction unit 13 by removing or suppressing the advancing-wave component is outputted as an advancing-wave removed time-domain signal.
As shown in FIG. 1, the variable coefficient IIR filter 14 includes a subtraction unit 21 and a variable coefficient FIR filter 22. The advancing-wave removed time-domain signal outputted from the subtraction unit 13 is supplied to the subtraction unit 21.
The subtraction unit 21 subtracts a replica of a multipath component (hereinafter, referred to as a delay wave) arriving later than a dominant wave from the advancing-wave removed time-domain signal which has been supplied from the variable coefficient FIR filter 22, thereby removing a delay-wave component included in the advancing-wave removed time-domain signal. A delay wave removed time-domain signal generated by the subtraction unit 21 by removing the delay-wave component is supplied to the variable coefficient FIR filter 22 as well as supplied to a subsequent stage of the equalizer 1.
The variable coefficient FIR filter 22 performs filtering to the signal supplied from the subtraction unit 21 by using a coefficient generated by a not-shown coefficient update circuit to thereby generate a delay-wave replica. The delay-wave replica generated by the variable coefficient FIR filter 22 is supplied to the subtraction unit 21.
As described above, in the equalizer 1, the replicas of the multipath components are generated by controlling coefficients of the variable coefficient FIR filters 11, 22 and the multipath components included in a received signal are removed by using replicas of multipath components.
An example of the related art includes JP-A-2005-150839 (Patent Document 1).